1. Field of the Invention
The present invention relates to a battery pack.
2. Description of the Related Art
Secondary batteries are rechargeable and can be used repeatedly, unlike disposable batteries which cannot be reused after complete discharge.
Such secondary batteries are widely used in handheld electronic devices such as personal digital assistants (PDAs), camcorders, cellular phones, notebook computers and MP3 players.
Particularly, lithium secondary batteries are widely used because they have a high operating voltage, a high energy density per unit weight and capacity, and because they can be compact.
Lithium secondary batteries may be manufactured in various shapes, for example, a cylindrical shape, a rectangular shape or a pouch shape.
Lithium secondary batteries typically include an outer casing and an electrode assembly sealed within the outer casing.
The electrode assembly is formed by sequentially stacking and winding a positive electrode plate, a separator and a negative electrode plate.
In the cylindrical- or rectangular-type secondary battery, the outer casing is sealed by a cap assembly.
In the pouch-type secondary battery, the outer casing is sealed at its edge.
The secondary battery formed as such is generally called a bare cell, and a secondary battery including one or more bare cells formed in a pack is called a battery pack.
A battery pack including a plurality of bare cells may be formed by attaching a frame case having only an outer frame to the plurality of bare cells connected to each other.
However, the battery pack described above is vulnerable to fracture or dislodging of the bare cells by external impact at a connection section between the bare cells.
Alternatively, the battery pack may be formed by inserting the plurality of bare cells connected to each other into rectangular-type upper and lower injection cases, and coupling these cases to each other.
As the plurality of bare cells are connected to each other, with narrow side surfaces of the bare cells being in contact, the entire wide side surface of the bare cells connected to each other becomes far broader.
Therefore, a wide surface of the injection case into which the plurality of bare cells are inserted becomes far broader. Hence, since a wide surface of the injection case is vulnerable to the external impact, forming a thin case through injection molding is difficult. Thus, the thickness of the battery pack may be greater than desired.